Term 2: Oblique-slip systems

Question 1

Transpressional and Transtensional deformation

Answer 1

Transpression (TP) causes the long axes of the strain
 ellipse to form at a lower angle to the PDZ.

Transtension (TT) – long axes forms at higher angle to the PDZ

both also involve a vertical component of deformation so get complex 3D patterns

Question 2

Types of deformation in oblique systems

Answer 2

In oblique compressional systems, strain may be homogeneous or partitioned into domains of wrench & pure shear-dominated deformation

Homogenous produces incline folds
Partitioned produces echelon folds

Question 3

Strike-slip shuffle

Answer 3

TRANSPRESSION
 During evolution of a major continental transform, pieces of crust may be sliced off and moved along the margin
 They may be accreted elsewhere on the margin after having been displaced for 100-1000s of km
 Makes it difficult to reconstruct history in ancient orogenic belts
Strike slip terrane tectonics: Western USA cordillera

Question 4

Escape tectonics

Answer 4

Continent-continent collision where lithospheric blocks move laterally out of the collision zone
e.g. Himilayan Orogeny

Question 5

Vertical and horizontal partitioning

Answer 5

TRANSPRESSION
Depending on lithology and temperature (rheology) various types of partitioning may take place vertically through the lithosphere
Here, strain partitioned in upper crust overlying homogeneous transpression in lithosphere
e.g Central California

Question 6

Transtension

Answer 6

Extension and strike slip at the same time

Question 7

Transtension in the Northumberland basin

Answer 7

Late Carboniferous strain is highly heterogenous due to kinematic partitioning
2 structurally distinct domains are identified

Wrench dominated domains (WDD) - twisted rocks
Extension dominated domains (EDD) - extension of rocks

Question 8

WDD structures

Answer 8

Vertical and horizontal shortening
Wrench dominated domains

dextral strike-slip faults are the dominant structures
at both regional and outcrop scale

Styolites, reverse faults, folds

Question 9

EDD structures

Answer 9

Vertical shortening - Conjugate normal faults